I have this issue on 17.10 and 18.04 but I'm not sure if it's related to the original reporter's case because for me I suspect it's related to amdgpu-pro. In earlier distributions the memory leak was elsewhere - I can't remember if it was in xorg or plasmashell, though. I *think* it also happened with fglrx, before amdgpu was released, but that was so long ago now I can't be sure.
Regardless, the way I work around this is to restart the polkitd service every now and then. Otherwise, after a few days the memory usage is in the order of *gigabytes*!
I have this issue on 17.10 and 18.04 but I'm not sure if it's related to the original reporter's case because for me I suspect it's related to amdgpu-pro. In earlier distributions the memory leak was elsewhere - I can't remember if it was in xorg or plasmashell, though. I *think* it also happened with fglrx, before amdgpu was released, but that was so long ago now I can't be sure.
Regardless, the way I work around this is to restart the polkitd service every now and then. Otherwise, after a few days the memory usage is in the order of *gigabytes*!